1. Field of the Invention
The present invention relates generally to internal combustion engines, and more particularly relates to techniques for sensing the position of a needle or poppet valve in order to maximize the efficiency of engine operation and reduce unwanted exhaust emissions.
2. Description of the Prior Art
Diesel engines typically employ needle valves which are open and closed at timed intervals to inject desired amounts of fuel into the cylinder for combustion. In order to maximize fuel efficiency and minimize undesirable exhaust emissions, it is necessary to detect the opening of the needle valve in relation to the engine crankshaft position. The opening of the needle valve can then be set or controlled in timed relationship to the engine crankshaft position.
Known needle valves generally include a needle and a related needle seat. When the needle is in contact with the seat, the valve is closed. When the needle is lifted off the seat, the valve opens and fuel is metered through orifices into the engine cylinder. The initial displacement between the needle and its corresponding seat determine the beginning of injection. It is necessary to time or control the initial displacement of the needle from the seat relative to the rotational position of the engine crankshaft, in order to maximize fuel efficiency, and at the same time reduce undesirable emissions.
It is known to determine timing by reference to visual markings on the engine flywheel. Techniques have also been developed to electronically measure the injection timing by determining needle position using inductive or capacitor devices positioned within a fuel injector nozzle holder.
Creative Tool Company of Lyons, Ill. presently manufactures a product known as the "Diesel TacTime CT 4000". This device utilizes a split-nut transducer which is installed on an engine cylinder fuel line at either the injection pump or at the nozzle. Mechanical strains produced by pulses of fuel through the fuel line create a mechanical displacement of the line which is detected by the transducer.